1. Field of the Invention
The present invention relates generally to the rate matching of a channel encoded signal, and in particular, to an apparatus and method for controlling a demultiplexer (DEMUX) and a multiplexer (MUX) used for rate matching.
2. Description of the Related Art
In general, radio communication systems, such as satellite, ISDN (Integrated Services Digital Network), W-CDMA (Wide band-Code Division Multiple Access), UMTS (Universal Mobile Telecommunication System), and IMT (International Mobile Telecommunication)-2000 systems, channel-encode source user data with an error correction code prior to transmission, in order to increase system reliability. Typical codes used for channel encoding are convolutional codes and linear blocks code for which a single decoder is used. Lately, turbo codes, which are useful for data transmission and reception, have been suggested.
A multiple-access and multiple-channel communication system matches the number of channel encoded symbols to a given number of transmission data symbols to increase data transmission efficiency and system performance. This operation is called rate matching. Puncturing and repetition are widely performed to match the data rate of channel encoded symbols. Rate matching has recently emerged as a significant factor in UMTS for increasing data transmission efficiency in the air interface and for improving system performance.
FIG. 1 is a block diagram of an uplink transmitting device in a general mobile communication system (a UMTS system, herein).
Referring to FIG. 1, a channel encoder 110 receives frame data at predetermined TTIs (Transmission Time Intervals) which may be 10, 20, 40, or 80 ms, and encodes the received frame data. And the channel encoder 110 outputs encoded symbols according to a predetermined coding rate R. The frame data size (number of information bits) is determined by a (data rate of the frame data)*(TTI). If tail bits are not considered, the number of encoded symbols are determined by the (frame data size)*(coding rate R). A 1st interleaver 120 interleaves the output of the channel encoder 110. A radio frame segmenter 130 segments interleaved symbols received from the 1st interleaver 120 into 10-ms radio frame blocks of which size is determined by (the number of encoded symbols)/(10), wherein 10 is the radio frame length unit. A rate matcher 140 matches the data rate of a radio frame received from the radio frame segmenter 130 to a preset data rate by puncturing or repeating symbols of the radio frame. The above-described components can be provided for each service.
A MUX 150 multiplexes rate-matched radio frames from each service. A physical channel segmenter 160 segments the multiplexed radio frames received from the MUX 150 into physical channel blocks. A 2nd interleaver 170 interleaves the physical channel blocks received from the physical channel segmenter 160. A physical channel mapper 180 maps the 2nd-interleaved blocks on physical channels for transmission.
As shown in FIG. 1, the UMTS uplink transmitting device is provided with rate matchers 140. The rate matcher 140 varies in configuration depending on whether the channel encoder 110 is a convolutional encoder or a turbo encoder.
When a linear block code is used (a convolutional encoder and a single decoder are used in this case) for the channel encoder, the following requirements of rate matching should be satisfied to increase data transmission efficiency and system performance in a multiple-access/multiple-channel scheme.
1. An input symbol sequence is punctured/repeated in a predetermined periodic pattern.
2. The number of punctured symbols is minimized whereas the number of repeated symbols is maximized.
3. A uniform puncturing/repeating pattern is used to puncture/repeat encoded symbols uniformly.
The above requirements are set on the assumption that the error sensitivity of a code symbol at any position in one frame output from a convolutional encoder is similar. Although some favorable results can be produced using the above requirements, a rate matching scheme different from the convolutional encoder should be employed when using a turbo encoder because of the different error sensitivities of symbols at different positions in one frame.
When a turbo encoder is used, it is preferred that the systematic information part of the encoded symbols is not punctured since the turbo encoder is a systematic encoder. Due to the two component encoder structure of the turbo encoder, the minimum free distance of the output code is maximized when the minimum free distance of each of the two component codes is maximized. To do so, the output symbols of the two component encoders should be punctured equally to thereby achieve optimal performance.
As described above, a distinction should be made between the information symbols and the parity symbols in the encoded symbols when a turbo encoder is used, to achieve optimal rate matching. Processing, such as channel interleaving, can be interposed between the turbo encoder and a rate matcher. Nevertheless, the distinction between information symbols and parity symbols should be preserved. However, this is impossible because all of the channel encoded symbols are randomly mixed after channel interleaving.